Transformed cells have higher levels of plasminogen activator activity than their normal cell counterparts. The major difficulty in studying the role of this enzyme in tumorigenicity and metastasis has been the lack of sensitive, quantitative assays. We synthesized several new organic compounds and with them developed sensitive, quantitative assays for the activation of plasminogen. Initially, we focused on the variables in the assays. We have shown that cell-associated plasminogen activators activate one form of plasminogen 10-fold more efficiently than others, that the plasminogen activator activity per cell decreases in inverse proportion to cell density at high cell densities, but not low, and that the close presence of one cell type can dramatically influence the plasminogen activator activity of another cell type. We have also been studying the induction of plasminogen activator activity by estrogens in the immature rat uterus and in human breast cancer cells and the effect of anti-estrogens on induction. Other studies have led us to propose a model for the targeting of plasminogen activator activity, which postulates that both a plasminogen activator and a plasmin substrate to which plasminogen is bound must be present simultaneously for activation of plasminogen to occur. Predictions from the model are currently being tested. The assay will be used to determine the degree of correlation between plasminogen activator activity and tumorigenicity and metastasis. Variations of the assay will be used to screen for mutants in plasminogen activator activity. A major objective is to develop a carcinogen assay that will be simple to perform and be as quick and sensitive as the Ames assay for mutagens. We shall also pursue the use of induction of plasminogen activator activity in human breast cancer cells by estrogens as a marker for endocrine-responsive tumor cells. (E)